Recovering affinity with imposter slices

ABSTRACT

Methods and apparatus for accessing dispersed storage error encoded data in a dispersed storage network (DSN). For each available primary storage unit, a processing module issues a write slice request including a slice name and encoded data slice corresponding to the primary storage unit where the encoded data slice includes an information dispersal algorithm (IDA) index of the primary storage unit. For each unavailable primary storage unit, the processing module issues a write imposter slice request to a foster storage unit that includes a slice name corresponding to foster storage unit and an imposter encoded data slice corresponding to the unavailable primary storage unit, where the imposter encoded data slice includes an IDA index corresponding to the unavailable primary storage unit. When the unavailable primary storage unit becomes available, the processing module facilitates transfer of the imposter encoded data slice to the newly available primary storage unit.

CROSS REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/248,752, filed30 Oct. 2015, entitled “MIGRATING DATA IN A DISPERSED STORAGE NETWORK,”which is hereby incorporated herein by reference in its entirety andmade part of the present U.S. Utility Patent Application for allpurposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTION

Technical Field of the Invention

This invention relates generally to computer networks, and moreparticularly to cloud storage.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on a remote storagesystem. The remote storage system may include a RAID (redundant array ofindependent disks) system and/or a dispersed storage system that uses anerror correction scheme to encode data for storage.

In a RAID system, a RAID controller adds parity data to the originaldata before storing it across an array of disks. The parity data iscalculated from the original data such that the failure of a single disktypically will not result in the loss of the original data. While RAIDsystems can address certain memory device failures, these systems maysuffer from effectiveness, efficiency and security issues. For instance,as more disks are added to the array, the probability of a disk failurerises, which may increase maintenance costs. When a disk fails, forexample, it needs to be manually replaced before another disk(s) failsand the data stored in the RAID system is lost. To reduce the risk ofdata loss, data on a RAID device is often copied to one or more otherRAID devices. While this may reduce the possibility of data loss, italso raises security issues since multiple copies of data may beavailable, thereby increasing the chances of unauthorized access. Inaddition, co-location of some RAID devices may result in a risk of acomplete data loss in the event of a natural disaster, fire, powersurge/outage, etc.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) in accordance with the presentdisclosure;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present disclosure;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present disclosure;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present disclosure;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present disclosure;

FIG. 6 is a schematic block diagram of an example of slice naminginformation for an encoded data slice (EDS) in accordance with thepresent disclosure;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present disclosure;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present disclosure;

FIG. 9 is a schematic block diagram of an example of a dispersed storagenetwork in accordance with the present disclosure;

FIG. 10A is a schematic block diagram of an embodiment of adecentralized agreement module in accordance with the present invention;

FIG. 10B is a flowchart illustrating an example of selecting theresource in accordance with the present invention;

FIG. 10C is a schematic block diagram of an embodiment of a dispersedstorage network (DSN) in accordance with the present invention;

FIG. 10D is a flowchart illustrating an example of accessing a dispersedstorage network (DSN) memory in accordance with the present invention;

FIG. 11A is a schematic block diagram of another embodiment of adispersed storage network (DSN) in accordance with the presentinvention;

FIG. 11B is a schematic block diagram of another embodiment of adispersed storage network (DSN) in accordance with the presentinvention; and

FIG. 11C is a flowchart illustrating an example of accessing data inaccordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofdispersed storage (DS) computing devices or processing units 12-16, amanaging unit 18, an integrity processing unit 20, and a DSN memory 22.The components of the DSN 10 are coupled to a network 24, which mayinclude one or more wireless and/or wire lined communication systems;one or more non-public intranet systems and/or public internet systems;and/or one or more local area networks (LAN) and/or wide area networks(WAN).

The DSN memory 22 includes a plurality of dispersed storage units 36 (DSunits) that may be located at geographically different sites (e.g., onein Chicago, one in Milwaukee, etc.), at a common site, or a combinationthereof. For example, if the DSN memory 22 includes eight dispersedstorage units 36, each storage unit is located at a different site. Asanother example, if the DSN memory 22 includes eight storage units 36,all eight storage units are located at the same site. As yet anotherexample, if the DSN memory 22 includes eight storage units 36, a firstpair of storage units are at a first common site, a second pair ofstorage units are at a second common site, a third pair of storage unitsare at a third common site, and a fourth pair of storage units are at afourth common site. Note that a DSN memory 22 may include more or lessthan eight storage units 36.

Each of the DS computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, and network orcommunications interfaces 30-33 which can be part of or external tocomputing core 26. DS computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the dispersed storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 and 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data (e.g., data object 40) as subsequently describedwith reference to one or more of FIGS. 3-8. In this example embodiment,computing device 16 functions as a dispersed storage processing agentfor computing device 14. In this role, computing device 16 dispersedstorage error encodes and decodes data on behalf of computing device 14.With the use of dispersed storage error encoding and decoding, the DSN10 is tolerant of a significant number of storage unit failures (thenumber of failures is based on parameters of the dispersed storage errorencoding function) without loss of data and without the need for aredundant or backup copies of the data. Further, the DSN 10 stores datafor an indefinite period of time without data loss and in a securemanner (e.g., the system is very resistant to unauthorized attempts ataccessing the data).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-16 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSN memory 22 fora user device, a group of devices, or for public access and establishesper vault dispersed storage (DS) error encoding parameters for a vault.The managing unit 18 facilitates storage of DS error encoding parametersfor each vault by updating registry information of the DSN 10, where theregistry information may be stored in the DSN memory 22, a computingdevice 12-16, the managing unit 18, and/or the integrity processing unit20. The DS error encoding parameters (e.g., or dispersed storage errorcoding parameters) include data segmenting information (e.g., how manysegments data (e.g., a file, a group of files, a data block, etc.) isdivided into), segment security information (e.g., per segmentencryption, compression, integrity checksum, etc.), error codinginformation (e.g., pillar width, decode threshold, read threshold, writethreshold, etc.), slicing information (e.g., the number of encoded dataslices that will be created for each data segment); and slice securityinformation (e.g., per encoded data slice encryption, compression,integrity checksum, etc.).

The managing unit 18 creates and stores user profile information (e.g.,an access control list (ACL)) in local memory and/or within memory ofthe DSN memory 22. The user profile information includes authenticationinformation, permissions, and/or the security parameters. The securityparameters may include encryption/decryption scheme, one or moreencryption keys, key generation scheme, and/or data encoding/decodingscheme.

The managing unit 18 creates billing information for a particular user,a user group, a vault access, public vault access, etc. For instance,the managing unit 18 tracks the number of times a user accesses anon-public vault and/or public vaults, which can be used to generateper-access billing information. In another instance, the managing unit18 tracks the amount of data stored and/or retrieved by a user deviceand/or a user group, which can be used to generate per-data-amountbilling information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network operations can furtherinclude monitoring read, write and/or delete communications attempts,which attempts could be in the form of requests. Network administrationincludes monitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

To support data storage integrity verification within the DSN 10, theintegrity processing unit 20 (and/or other devices in the DSN 10 such asmanaging unit 18) may assess and perform rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. Retrieved encoded slices are assessed and checked for errorsdue to data corruption, outdated versioning, etc. If a slice includes anerror, it is flagged as a ‘bad’ or ‘corrupt’ slice. Encoded data slicesthat are not received and/or not listed may be flagged as missingslices. Bad and/or missing slices may be subsequently rebuilt usingother retrieved encoded data slices that are deemed to be good slices inorder to produce rebuilt slices. A multi-stage decoding process may beemployed in certain circumstances to recover data even when the numberof valid encoded data slices of a set of encoded data slices is lessthan a relevant decode threshold number. The rebuilt slices may then bewritten to DSN memory 22. Note that the integrity processing unit 20 maybe a separate unit as shown, included in DSN memory 22, included in thecomputing device 16, managing unit 18, stored on a DS unit 36, and/ordistributed among multiple storage units 36.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the IO deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment (i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber. In the illustrated example, the value X11=aD1+bD5+cD9,X12=aD2+bD6+cD10, . . . X53=mD3+nD7+oD11, and X54=mD4+nD8+oD12.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 80 is shown inFIG. 6. As shown, the slice name (SN) 80 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as at least part of a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

In order to recover a data segment from a decode threshold number ofencoded data slices, the computing device uses a decoding function asshown in FIG. 8. As shown, the decoding function is essentially aninverse of the encoding function of FIG. 4. The coded matrix includes adecode threshold number of rows (e.g., three in this example) and thedecoding matrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a diagram of an example of a dispersed storage network. Thedispersed storage network includes a DS (dispersed storage) clientmodule 34 (which may be in DS computing devices 12 and/or 16 of FIG. 1),a network 24, and a plurality of DS units 36-1 . . . 36-n (which may bestorage units 36 of FIG. 1 and which form at least a portion of DSmemory 22 of FIG. 1), a DSN managing unit (not shown—device 18 in FIG.1), and a DS integrity verification module 20. The DS client module 34includes an outbound DS processing section 81 and an inbound DSprocessing section 82. Each of the DS units 36-1 . . . 36-n includes acontroller 86, a processing module 84 including a communicationsinterface for communicating over network 24 (not shown), memory 88, a DT(distributed task) execution module 90, and a DS client module 34.

In an example of operation, the DS client module 34 receives data 92.The data 92 may be of any size and of any content, where, due to thesize (e.g., greater than a few Terabytes), the content (e.g., securedata, etc.), and/or concerns over security and loss of data, distributedstorage of the data is desired. For example, the data 92 may be one ormore digital books, a copy of a company's emails, a large-scale Internetsearch, a video security file, one or more entertainment video files(e.g., television programs, movies, etc.), data files, and/or any otherlarge amount of data (e.g., greater than a few Terabytes).

Within the DS client module 34, the outbound DS processing section 81receives the data 92. The outbound DS processing section 81 processesthe data 92 to produce slice groupings 96. As an example of suchprocessing, the outbound DS processing section 81 partitions the data 92into a plurality of data partitions. For each data partition, theoutbound DS processing section 81 dispersed storage (DS) error encodesthe data partition to produce encoded data slices and groups the encodeddata slices into a slice grouping 96.

The outbound DS processing section 81 then sends, via the network 24,the slice groupings 96 to the DS units 36-1 . . . 36-n of the DSN memory22 of FIG. 1. For example, the outbound DS processing section 81 sendsslice group to DS storage unit 36-1. As another example, the outbound DSprocessing section 81 sends slice group #n to DS unit #n.

In one example of operation, the DS client module 34 requests retrievalof stored data within the memory of the DS units 36. In this example,the task 94 is retrieve data stored in the DSN memory 22. Accordingly,and according to one embodiment, the outbound DS processing section 81converts the task 94 into a plurality of partial tasks 98 and sends thepartial tasks 98 to the respective DS storage units 36-1 . . . 36-n.

In response to the partial task 98 of retrieving stored data, a DSstorage unit 36 identifies the corresponding encoded data slices 99 andretrieves them. For example, DS unit #1 receives partial task #1 andretrieves, in response thereto, retrieved slices #1. The DS units 36send their respective retrieved slices 99 to the inbound DS processingsection 82 via the network 24.

The inbound DS processing section 82 converts the retrieved slices 99into data 92. For example, the inbound DS processing section 82de-groups the retrieved slices 99 to produce encoded slices per datapartition. The inbound DS processing section 82 then DS error decodesthe encoded slices per data partition to produce data partitions. Theinbound DS processing section 82 de-partitions the data partitions torecapture the data 92.

FIG. 10A is a schematic block diagram of an embodiment of adecentralized agreement module 350 that includes a set of deterministicfunctions 340-1 . . . 340-N, a set of normalizing functions 342-1 . . .342-N, a set of scoring functions 344-1 . . . 344-N, and a rankingfunction 352. Each of the deterministic function, the normalizingfunction, the scoring function, and the ranking function 352, may beimplemented utilizing the processing module 84 of FIG. 9. Thedecentralized agreement module 350 may be implemented utilizing anymodule and/or unit of a dispersed storage network (DSN). For example,the decentralized agreement module is implemented utilizing thedistributed storage (DS) client module 34 of FIG. 1.

The decentralized agreement module 350 functions to receive a rankedscoring information request 354 and to generate ranked scoringinformation 358 based on the ranked scoring information request 354 andother information. The ranked scoring information request 354 includesone or more of an asset identifier (ID) 356 of an asset associated withthe request, an asset type indicator, one or more location identifiersof locations associated with the DSN, one or more corresponding locationweights, and a requesting entity ID. The asset includes any portion ofdata associated with the DSN including one or more asset types includinga data object, a data record, an encoded data slice, a data segment, aset of encoded data slices, and a plurality of sets of encoded dataslices. As such, the asset ID 356 of the asset includes one or more of adata name, a data record identifier, a source name, a slice name, and aplurality of sets of slice names.

Each location of the DSN includes an aspect of a DSN resource. Examplesof locations include one or more of a storage unit, a memory device ofthe storage unit, a site, a storage pool of storage units, a pillarindex associated with each encoded data slice of a set of encoded dataslices generated by an information dispersal algorithm (IDA), a DSclient module 34 of FIG. 1, a DS processing unit (computing device) 16of FIG. 1, a DS integrity processing unit 20 of FIG. 1, a DSN managingunit 18 of FIG. 1, a user device (computing device) 12 of FIG. 1, and auser device (computing device) 14 of FIG. 1.

Each location is associated with a location weight based on one or moreof a resource prioritization of utilization scheme and physicalconfiguration of the DSN. The location weight includes an arbitrary biaswhich adjusts a proportion of selections to an associated location suchthat a probability that an asset will be mapped to that location isequal to the location weight divided by a sum of all location weightsfor all locations of comparison. For example, each storage pool of aplurality of storage pools is associated with a location weight based onstorage capacity. For instance, storage pools with more storage capacityare associated with higher location weights than others. The otherinformation may include a set of location identifiers and a set oflocation weights associated with the set of location identifiers. Forexample, the other information includes location identifiers andlocation weights associated with a set of memory devices of a storageunit when the requesting entity utilizes the decentralized agreementmodule 350 to produce ranked scoring information 358 with regards toselection of a memory device of the set of memory devices for accessinga particular encoded data slice (e.g., where the asset ID includes aslice name of the particular encoded data slice).

The decentralized agreement module 350 outputs substantially identicalranked scoring information for each ranked scoring information requestthat includes substantially identical content of the ranked scoringinformation request. For example, a first requesting entity issues afirst ranked scoring information request to the decentralized agreementmodule 350 and receives first ranked scoring information. A secondrequesting entity issues a second ranked scoring information request tothe decentralized agreement module and receives second ranked scoringinformation. The second ranked scoring information is substantially thesame as the first ranked scoring information when the second rankedscoring information request is substantially the same as the firstranked scoring information request.

As such, two or more requesting entities may utilize the decentralizedagreement module 350 to determine substantially identical ranked scoringinformation. As a specific example, the first requesting entity selectsa first storage pool of a plurality of storage pools for storing a setof encoded data slices utilizing the decentralized agreement module 350and the second requesting entity identifies the first storage pool ofthe plurality of storage pools for retrieving the set of encoded dataslices utilizing the decentralized agreement module 350.

In an example of operation, the decentralized agreement module 350receives the ranked scoring information request 354. Each deterministicfunction performs a deterministic function on a combination and/orconcatenation (e.g., add, append, interleave) of the asset ID 356 of theranked scoring information request 354 and an associated location ID ofthe set of location IDs to produce an interim result 341-1 . . . 341-N.The deterministic function includes at least one of a hashing function,a hash-based message authentication code function, a mask generatingfunction, a cyclic redundancy code function, hashing module of a numberof locations, consistent hashing, rendezvous hashing, and a spongefunction. As a specific example, deterministic function 340-2 appends alocation ID 339-2 of a storage pool to a source name as the asset ID toproduce a combined value and performs the mask generating function onthe combined value to produce interim result 341-2.

With a set of interim results 341-1 . . . 341-N, each normalizingfunction 342-1 . . . 342N performs a normalizing function on acorresponding interim result to produce a corresponding normalizedinterim result. The performing of the normalizing function includesdividing the interim result by a number of possible permutations of theoutput of the deterministic function to produce the normalized interimresult. For example, normalizing function 342-2 performs the normalizingfunction on the interim result 341-2 to produce a normalized interimresult 343-2.

With a set of normalized interim results 343-1 . . . 343-N, each scoringfunction performs a scoring function on a corresponding normalizedinterim result to produce a corresponding score. The performing of thescoring function includes dividing an associated location weight by anegative log of the normalized interim result. For example, scoringfunction 344-2 divides location weight 345-2 of the storage pool (e.g.,associated with location ID 339-2) by a negative log of the normalizedinterim result 343-2 to produce a score 346-2.

With a set of scores 346-1 . . . 346-N, the ranking function 352performs a ranking function on the set of scores 346-1 . . . 346-N togenerate the ranked scoring information 358. The ranking functionincludes rank ordering each score with other scores of the set of scores346-1 . . . 346-N, where a highest score is ranked first. As such, alocation associated with the highest score may be considered a highestpriority location for resource utilization (e.g., accessing, storing,retrieving, etc., the given asset of the request). Having generated theranked scoring information 358, the decentralized agreement module 350outputs the ranked scoring information 358 to the requesting entity.

FIG. 10B is a flowchart illustrating an example of selecting a resource.The method begins or continues at step 360 where a processing module(e.g., of a decentralized agreement module) receives a ranked scoringinformation request from a requesting entity with regards to a set ofcandidate resources. For each candidate resource, the method continuesat step 362 where the processing module performs a deterministicfunction on a location identifier (ID) of the candidate resource and anasset ID of the ranked scoring information request to produce an interimresult. As a specific example, the processing module combines the assetID and the location ID of the candidate resource to produce a combinedvalue and performs a hashing function on the combined value to producethe interim result.

For each interim result, the method continues at step 364 where theprocessing module performs a normalizing function on the interim resultto produce a normalized interim result. As a specific example, theprocessing module obtains a permutation value associated with thedeterministic function (e.g., maximum number of permutations of outputof the deterministic function) and divides the interim result by thepermutation value to produce the normalized interim result (e.g., with avalue between 0 and 1).

For each normalized interim result, the method continues at step 366where the processing module performs a scoring function on thenormalized interim result utilizing a location weight associated withthe candidate resource associated with the interim result to produce ascore of a set of scores. As a specific example, the processing moduledivides the location weight by a negative log of the normalized interimresult to produce the score.

The method continues at step 368 where the processing module rank ordersthe set of scores to produce ranked scoring information (e.g., ranking ahighest value first). The method continues at step 370 where theprocessing module outputs the ranked scoring information to therequesting entity. The requesting entity may utilize the ranked scoringinformation to select one location of a plurality of locations.

FIG. 10C is a schematic block diagram of an embodiment of a dispersedstorage network (DSN) that includes the distributed storage (DS)processing unit (computing device) 16 of FIG. 1, the network 24 of FIG.1, and the distributed storage network (DSN) module 22 of FIG. 1.Hereafter, the DSN module 22 may be interchangeably referred to as a DSNmemory. The DS processing unit 16 includes a decentralized agreementmodule 380 and the DS client module 34 of FIG. 1. The decentralizedagreement module 380 being implemented utilizing the decentralizedagreement module 350 of FIG. 10A. The DSN module 22 includes a pluralityof DS unit pools 400-1 . . . 400-N. Each DS unit pool includes one ormore sites 402-1 . . . 402-N. Each site includes one or more DS units404-1-1 . . . 404-1-N. Each DS unit may be associated with at least onepillar of N pillars associated with an information dispersal algorithm(IDA) (406-1 . . . 406-N), where a data segment is dispersed storageerror encoded using the IDA to produce one or more sets of encoded dataslices, and where each set includes N encoded data slices and likeencoded data slices (e.g., slice 3's) of two or more sets of encodeddata slices are included in a common pillar (e.g., pillar 406-3). Eachsite may not include every pillar and a given pillar may be implementedat more than one site. Each DS unit includes a plurality of memories(e.g. DS unit 404-1-1 includes memories 408-1-1-1 . . . 408-1-1-N. EachDS unit may be implemented utilizing the DS unit 36 of FIG. 1 and thememories 408 of DS units can be implemented utilizing memory 88 of DSunit 36 in FIG. 9. Hereafter, a DS unit may be referred tointerchangeably as a storage unit and a set of DS units may beinterchangeably referred to as a set of storage units and/or as astorage unit set.

The DSN functions to receive data access requests 382, select resourcesof at least one DS unit pool for data access, utilize the selected DSunit pool for the data access, and issue a data access response 392based on the data access. The selecting of the resources includesutilizing a decentralized agreement function of the decentralizedagreement module 380, where a plurality of locations are ranked againsteach other. The selecting may include selecting one storage pool of theplurality of storage pools, selecting DS units at various sites of theplurality of sites, selecting a memory of the plurality of memories foreach DS unit, and selecting combinations of memories, DS units, sites,pillars, and storage pools.

In an example of operation, the DS client module 34 receives the dataaccess request 382 from a requesting entity, where the data accessrequest 382 includes at least one of a store data request, a retrievedata request, a delete data request, a data name, and a requestingentity identifier (ID). Having received the data access request 382, theDS client module 34 determines a DSN address associated with the dataaccess request. The DSN address includes at least one of a source name(e.g., including a vault ID and an object number associated with thedata name), a data segment ID, a set of slice names, a plurality of setsof slice names. The determining includes at least one of generating(e.g., for the store data request) and retrieving (e.g., from a DSNdirectory, from a dispersed hierarchical index) based on the data name(e.g., for the retrieve data request).

Having determined the DSN address, the DS client module 34 selects aplurality of resource levels (e.g., DS unit pool, site, DS unit, pillar,memory) associated with the DSN module 22. The determining may be basedon one or more of the data name, the requesting entity ID, apredetermination, a lookup, a DSN performance indicator, andinterpreting an error message. For example, the DS client module 34selects the DS unit pool as a first resource level and a set of memorydevices of a plurality of memory devices as a second resource levelbased on a system registry lookup for a vault associated with therequesting entity.

Having selected the plurality of resource levels, the DS client module34, for each resource level, issues a ranked scoring information request384 to the decentralized agreement module 380 utilizing the DSN addressas an asset ID. The decentralized agreement module 380 performs thedecentralized agreement function based on the asset ID (e.g., the DSNaddress), identifiers of locations of the selected resource levels, andlocation weights of the locations to generate ranked scoring information386.

For each resource level, the DS client module 34 receives correspondingranked scoring information 386. Having received the ranked scoringinformation 386, the DS client module 34 identifies one or moreresources associated with the resource level based on the rank scoringinformation 386. For example, the DS client module 34 identifies a DSunit pool associated with a highest score and identifies a set of memorydevices within DS units of the identified DS unit pool with a highestscore.

Having identified the one or more resources, the DS client module 34accesses the DSN module 22 based on the identified one or more resourcesassociated with each resource level. For example, the DS client module34 issues resource access requests 388 (e.g., write slice requests whenstoring data, read slice requests when recovering data) to theidentified DS unit pool, where the resource access requests 388 furtheridentify the identified set of memory devices. Having accessed the DSNmodule 22, the DS client module 34 receives resource access responses390 (e.g., write slice responses, read slice responses). The DS clientmodule 34 issues the data access response 392 based on the receivedresource access responses 390. For example, the DS client module 34decodes received encoded data slices to reproduce data and generates thedata access response 392 to include the reproduced data.

FIG. 10D is a flowchart illustrating an example of accessing a dispersedstorage network (DSN) memory. The method begins or continues at step 410where a processing module (e.g., of a distributed storage (DS) clientmodule) receives a data access request from a requesting entity. Thedata access request includes one or more of a storage request, aretrieval request, a requesting entity identifier, and a data identifier(ID). The method continues at step 412 where the processing moduledetermines a DSN address associated with the data access request. Forexample, the processing module generates the DSN address for the storagerequest. As another example, the processing module performs a lookup forthe retrieval request based on the data identifier.

The method continues at step 414 where the processing module selects aplurality of resource levels associated with the DSN memory. Theselecting may be based on one or more of a predetermination, a range ofweights associated with available resources, a resource performancelevel, and a resource performance requirement level. For each resourcelevel, the method continues at step 416 where the processing moduledetermines ranked scoring information. For example, the processingmodule issues a ranked scoring information request to a decentralizedagreement module based on the DSN address and receives correspondingranked scoring information for the resource level, where thedecentralized agreement module performs a decentralized agreementprotocol function on the DSN address using the associated resourceidentifiers and resource weights for the resource level to produce theranked scoring information for the resource level.

For each resource level, the method continues at step 418 where theprocessing module selects one or more resources associated with theresource level based on the ranked scoring information. For example, theprocessing module selects a resource associated with a highest scorewhen one resource is required. As another example, the processing moduleselects a plurality of resources associated with highest scores when aplurality of resources are required.

The method continues at step 420 where the processing module accessesthe DSN memory utilizing the selected one or more resources for each ofthe plurality of resource levels. For example, the processing moduleidentifies network addressing information based on the selectedresources including one or more of a storage unit Internet protocoladdress and a memory device identifier, generates a set of encoded dataslice access requests based on the data access request and the DSNaddress, and sends the set of encoded data slice access requests to theDSN memory utilizing the identified network addressing information.

The method continues at step 422 where the processing module issues adata access response to the requesting entity based on one or moreresource access responses from the DSN memory. For example, theprocessing module issues a data storage status indicator when storingdata. As another example, the processing module generates the dataaccess response to include recovered data when retrieving data.

In one example of operation, the DSN of FIGS. 1 and/or 9 can be used toaccess data stored in the plurality of storage units. The accessingincludes storing the data and retrieving stored data to produce recoverdata. More specifically, as will be explained below in greater detail inconjunction with FIGS. 11A-C, the DSN can be used to recover affinityusing imposter slices.

In Foster Slice strategies including Trimmed Writes and Target Widths,affinity is the concept which balances utilization and maintainsavailability guarantees by spreading primary locations evenly across thefull set of possible storage locations. For example, in a Trimmed Writesscenario across 3 sites with Write Threshold of 33, Threshold of 20, andWidth of 54, there may be 18 DS units at each site. Since WriteThreshold is 33, 11 DS units at each site would be selected as theprimary location according to the affinity algorithm (whichdeterministically and fairly selects an affinity pattern based on thesource name). With any one site down, there remain 36 possible storagelocations in this example, so data may be stored with some site down andstill meet the write threshold of 33. However, when the site that wasdown returns online, should one of the two sites that were online gooffline, then data written at that time is no longer available. This isbecause in this failure pattern, no more than 18 slices will remainaccessible after a secondary site outage occurs. To restore tolerance ofa site outage, affinity must be restored. Affinity is restored when forevery source name stored in a DSN memory, each primary location for thatsource holds a slice for that source.

Restoring affinity may be either independently driven, or rebuilderdriven. When it is independently driven, each DS unit which holds aslice for which it is a “secondary” DS unit according to the affinityalgorithm, will periodically attempt to find a DS unit which is aprimary location for that source which does not hold a slice. When itfinds such a DS unit, it may transfer the slice it has to that primarylocation when using imposter slices. This may necessitate renaming ofthe slice such that the pillar index field within the slice name matchesthe range for which that DS unit is responsible. Once the slice has beensuccessfully transferred to the primary location, the secondary locationwhich transferred the slice must remove it's copy of the slice. When theprocess is rebuild driven, the rebuilder (for example a DS unit 36,Integrity Processing Unit 20, Managing Unit 18 and/or DS client module34) when considering the listing results of slice names held by DS unitsperforms the affinity function to the source name, to determine if anyof the listing results contain slices on secondary DS units and whenthere are primary DS units that are missing a slice they should have.When this situation is detected, the rebuilder may read those slicesfrom the secondary locations holding a slice, and re-write/rename theslices to primary locations lacking a slice. Alternatively, it may senda command to the DS unit instructing it of which slice to transfer towhich location. After the transfer, the rebuilder can then instruct theDS unit to delete that slice. Note that in cases where the slice beingtransferred is not currently wrapped with embedded information about thepillar the slice represents, the DS unit or the rebuilder may modify theslice (e.g. update the slice format and append a field indicating thepillar information) as part of the rename/transfer operation. Therefore,if the slice was not originally written with this extra information, itcan be added later as part of creating an imposter slice.

FIGS. 11A-B are schematic block diagrams of another embodiment of adispersed storage network (DSN) that includes a plurality of sites500-1, 500-2, and 500-3, the network 24 of FIG. 1, and the distributedstorage (DS) processing unit 16 of FIG. 1. Each site includes aplurality of storage units of a set of dispersed storage units 36-1 . .. 36-54. Each storage unit may be implemented utilizing the DS unit 36of FIG. 1. For example, the set of storage units includes 54 storageunits when an information dispersal algorithm (IDA), that is utilized toencode data for storage in the set of storage units, includes an IDAwidth of 54. For instance, 18 storage units are deployed at each sitewhen the number of sites is 3, the IDA width is 54, and an evendistribution approach for storage units to sites is utilized. The DSNfunctions to maintain access to stored data.

FIG. 11A illustrates steps of an example of operation of the maintainingof the access where the DS processing unit 16 dispersed storage errorencodes a data segment of data A 502 to produce at least a writethreshold number of encoded data slices of a set of encoded data slices.For example, the DS processing unit 16 dispersed storage error encodesthe data segment to produce 33 encoded data slices (a first through athirty-third) when the write threshold value of the informationdispersal algorithm is 33 and the IDA width is 54.

For each available primary dispersed storage unit of the set of storageunits, the DS processing unit 16 issues a respective write slice requestthat includes a respective slice name corresponding to a respectiveprimary storage unit and a respective encoded data slice correspondingto the respective primary storage unit, where the respective encodeddata slice includes a respective IDA index of, or corresponding to, therespective primary storage unit. The DS processing unit 16 designatesprimary storage units as storage units associated with the writethreshold number of encoded data slices of the set of encoded dataslices. For example, the DT processing unit 16 designates a first elevenstorage units of each plurality of storage units at each of the 3 sites(e.g., primary storage units: 36-1 to 36-11, 36-19 to 39-29, and 36-37to 36-47). As a specific example of the issuing of write slice requests,the DS processing unit 16 generates write slice requests 504-19 to504-29 and 504-37 to 504-47 to respectively include slice names of, orcorresponding to, storage units 36-19 to 36-29 and 36-37 to 36-47 (forthe nineteenth to twenty-ninth and thirty-seventh to forty-seventhencoded data slices respectively (not shown)), where the encoded dataslices are respectively embedded with respective IDA indexes (notshown). The DS processing unit 16 then sends, via the network 24, thewrite slice requests 504-19 to 504-29 and 504-37 to 504-47 to thestorage units 36-19 to 36-29 and 36-37 to 36-47 associated with sites500-2 and 500-3 when the storage units 36-19 to 36-29 and 36-37 to 36-47are available and the primary storage units includes the storage units36-1 to -11, 36-19 to 3629 and 36-37 to 36-47.

For each unavailable primary dispersed storage unit of the set ofstorage units, the DS processing unit 16 issues a respective writeimposter slice request to a respective foster storage unit that includesa respective imposter slice name corresponding to the respective fosterstorage unit and a respective imposter encoded data slice correspondingto the respective unavailable primary storage unit, where the respectiveimposter encoded data slice includes a respective IDA index of, orcorresponding to, the respective unavailable primary storage unit. Forexample, the DS processing unit 16 generates write imposter slicerequests 506-30:1 to 506-36:7 to include imposter slice names of, orcorresponding to, foster storage units 36-30 to 36-36 and imposterencoded data slices corresponding to unavailable primary storage units36-1 to 36-7 (i.e. the first to seventh encoded data slices (notshown)), where the imposter encoded data slices includes, or areembedded with, respective IDA indexes corresponding to the unavailableprimary storage unit 36-1 to 36-7. (not shown) Continuing with theexample, the DS processing unit 16 generates write imposter slicerequests 506-48:8 to 506-51:11 to include imposter slice names of, orcorresponding to, foster storage units 36-48 to 36-51 and imposterencoded data slices corresponding to unavailable primary storage units36-8 to 36-11 (i.e. the eighth to eleventh encoded data slices (notshown)), where the imposter encoded data slices includes, or areembedded with, respective IDA indexes corresponding to primary storageunits 36-8 to 36-11 (IDA indexes not shown). Having generated the writeimposter encoded data slice requests, the DS processing unit 16 sendsthe respective write imposter encoded data slice requests to therespective foster storage units. For example, the DS processing unit 16sends, via the network 24, the write imposter slice requests 506-30:1 to506-36:7 to the storage units 36-30 to 36-36 and sends, via the network24, the write imposter slice requests 506-48:8 to 506-51:11 to thestorage units 36-48 to 36-51.

FIG. 11B illustrates further steps of the example of operation of themaintaining of the access. When an unavailable primary storage unitbecomes a newly available primary storage unit, a foster storage unitfacilitates transfer of a corresponding imposter encoded data slice tothe newly available primary storage unit. For example, when the primarystorage units 36-1 to 36-11 become available, the respective fosterstorage units 36-30 to 36-36 send, via the network 24, the respectiveencoded data slices 508-1 to 508-7 (e.g., extracted from respectiveimposter encoded data slices not shown) to the respective primarystorage units 36-1 to 36-7 for storage. Continuing with the example, therespective foster storage units 36-48 to 36-51 send, via the network 24,the respective encoded data slices 508-8 to 508-11 (e.g., extracted fromrespective imposter encoded data slices not shown) to the storage units36-8 to 36-11 for storage. When detecting successful transfer of therespective encoded data slices of the imposter encoded data slices tothe now available primary storage units, the respective foster storageunits deletes the respective imposter encoded data slices. For example,foster storage units 36-30 to 36-36 respectively delete the imposterencoded data slices corresponding to encoded data slices 508-1 to 508-7and the foster storage units 36-48 to 36-51 respectively delete theimposter encoded data slices corresponding to encoded data slices 508-8to 508-11.

FIG. 11C is a flowchart illustrating an example of maintaining access tostored data. The method includes the step 600 where a processing moduleof a one or more processing modules of one or more computing devices(e.g., of a distributed storage (DS) processing unit) dispersed storageerror encodes a data segment of data to produce a set of encoded dataslices. For each available primary storage unit of a set of primarystorage units, the method continues at the 602 step where the processingmodule issues a write slice request that includes a slice name and aunique encoded data slice of the set of encoded data slicescorresponding to the primary storage unit, where the encoded data sliceincludes an information dispersal algorithm (IDA) index of the primarystorage unit. For example, a processing module generates a respectivewrite slice request to include the slice name corresponding to arespective primary storage unit and the encoded data slice correspondingto the respective primary storage unit embedded with the IDA index ofthe respective primary storage unit, and sends the write slice requestto the respective primary storage unit.

For each unavailable primary storage unit of the set of storage units,the method continues at the step 604 where the processing module issuesa write imposter slice request to a foster storage unit that includes animposter slice name corresponding to foster storage unit and an imposterencoded data slice corresponding to the unavailable primary storageunit, where the imposter encoded data slice includes an IDA indexcorresponding to the unavailable primary storage unit. For example, aprocessing module generates a respective write imposter slice request toinclude the imposter slice name corresponding to a respective fosterstorage unit and an imposter encoded data slice corresponding to arespective unavailable primary storage unit embedded with the IDA indexcorresponding to the respective unavailable primary storage unit,selects the respective foster storage unit (e.g., based on one or moreof a predetermination, storage unit availability, in accordance withsystem registry information), and sends the respective write imposterslice request to the respective foster storage unit.

When the unavailable primary storage unit becomes a newly availableprimary storage unit, the method continues at the step where theprocessing module facilitates transfer, via the foster storage unit, ofthe imposter encoded data slice corresponding to the newly availableprimary storage unit. For example, a foster storage unit generates awrite slice request that includes the encoded data slice correspondingto a respective newly available primary storage unit (e.g., whichincludes the IDA index of the respective newly available storage unit)and a slice name of the respective newly available storage unit, andsends the write slice request to the respective newly available primarystorage unit. In addition, when detecting successful transfer of animposter encoded data slice to the newly available primary storage unit,foster storage unit facilitates deletion of the imposter encoded dataslice from the foster storage unit.

The methods described above in conjunction with the computing device andthe storage units can alternatively be performed by other modules of thedispersed storage network or by other devices. For example, anycombination of a first module, a second module, a third module, a fourthmodule, etc. of the computing device and the storage units may performthe method described above. In addition, at least one memory section(e.g., a first memory section, a second memory section, a third memorysection, a fourth memory section, a fifth memory section, a sixth memorysection, etc. of a non-transitory computer readable storage medium) thatstores operational instructions can, when executed by one or moreprocessing modules of one or more computing devices and/or by thestorage units of the dispersed storage network (DSN), cause the one ormore computing devices and/or the storage units to perform any or all ofthe method steps described above.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent. Such relativitybetween items ranges from a difference of a few percent to magnitudedifferences. As may also be used herein, the term(s) “configured to”,“operably coupled to”, “coupled to”, and/or “coupling” includes directcoupling between items and/or indirect coupling between items via anintervening item (e.g., an item includes, but is not limited to, acomponent, an element, a circuit, and/or a module) where, for an exampleof indirect coupling, the intervening item does not modify theinformation of a signal but may adjust its current level, voltage level,and/or power level. As may further be used herein, inferred coupling(i.e., where one element is coupled to another element by inference)includes direct and indirect coupling between two items in the samemanner as “coupled to”. As may even further be used herein, the term“configured to”, “operable to”, “coupled to”, or “operably coupled to”indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signalA has a greater magnitude than signal B, a favorable comparison may beachieved when the magnitude of signal A is greater than that of signal Bor when the magnitude of signal B is less than that of signal A. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from Figureto Figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information. A computer readable memory/storage medium,as used herein, is not to be construed as being transitory signals perse, such as radio waves or other freely propagating electromagneticwaves, electromagnetic waves propagating through a waveguide or othertransmission media (e.g., light pulses passing through a fiber-opticcable), or electrical signals transmitted through a wire.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method of accessing data in a dispersed storagenetwork, the dispersed storage network including a plurality of primarydispersed storage units and a plurality of secondary dispersed storageunits, the method comprising: dispersed storage error encoding a datasegment to produce a set of encoded data slices; for each availableprimary dispersed storage unit of the plurality of primary dispersedstorage units, sending a respective write slice request for receipt by arespective available primary dispersed storage unit, the respectivewrite slice request including a respective slice name corresponding tothe respective available primary dispersed storage unit and a respectiveencoded data slice of the set of encoded data slices, wherein therespective encoded data slice includes a first respective informationdispersed algorithm index of the respective available primary dispersedstorage unit; and for each unavailable primary dispersed storage unit ofthe plurality of primary dispersed storage units, sending a respectivewrite imposter slice request for receipt by a respective secondarydispersed storage unit of the plurality of secondary dispersed storageunits, the respective write imposter slice request including arespective imposter slice name corresponding to the respective secondarydispersed storage unit and a respective imposter encoded data slice ofthe set of encoded data slices, wherein the respective imposter encodeddata slice includes a second respective information dispersed algorithmindex of the respective unavailable primary dispersed storage unit. 2.The method of claim 1, wherein the set of encoded data slices includesat least a write threshold number of encoded data slices.
 3. The methodof claim 2, wherein the plurality of primary dispersed storage units isequal to the number of encoded data slices in the set of encoded dataslices.
 4. The method of claim 1, further comprising sending a commandto one of the respective secondary dispersed storage units to send oneof the respective imposter encoded data slices to one of the respectiveunavailable primary dispersed storage units when the one of respectiveunavailable primary dispersed storage units becomes available.
 5. Themethod of claim 4, further comprising sending a command to the one ofthe respective secondary dispersed storage units to delete the one ofthe respective imposter encoded data slices.
 6. The method of claim 4,further comprising renaming the respective imposter encoded data slice.7. The method of claim 1 further including receiving one of therespective imposter encoded data slices from one of the respectivesecondary dispersed storage units and forwarding the one of therespective imposter encoded data slices to one of the respectiveunavailable primary dispersed storage units when the one of therespective unavailable primary dispersed storage units becomesavailable.
 8. The method of claim 7, further comprising sending acommand to the one of the respective secondary dispersed storage unitsto delete the one of the respective imposter encoded data slices.
 9. Themethod of claim 7, further comprising renaming the respective imposterencoded data slice.
 10. A dispersed storage processing unit for use in adispersed storage network, the dispersed storage network including aplurality of primary dispersed storage units and a plurality ofsecondary dispersed storage units, the first dispersed storageprocessing unit comprising: a communications interface; a memory; and aprocessor; wherein the memory includes a data segment and wherein thememory further includes instructions for causing the processor to:dispersed storage error encode a data segment to produce a set ofencoded data slices; for each available primary dispersed storage unitof the plurality of primary dispersed storage units, send a respectivewrite slice request for receipt by a respective available primarydispersed storage unit, the respective write slice request including arespective slice name corresponding to the respective available primarydispersed storage unit and a respective encoded data slice of the set ofencoded data slices, wherein the respective encoded data slice includesa respective information dispersed algorithm index of the respectiveavailable primary dispersed storage unit; and for each unavailableprimary dispersed storage unit of the plurality of primary dispersedstorage units, send a respective write imposter slice request forreceipt by a respective secondary dispersed storage unit of theplurality of secondary dispersed storage units, the respective writeimposter slice request including a respective imposter slice namecorresponding to the respective secondary dispersed storage unit and arespective imposter encoded data slice of the set of encoded dataslices, wherein the respective imposter encoded data slice includes arespective information dispersed algorithm index of the respectiveunavailable primary dispersed storage unit.
 11. The dispersed storageprocessing unit of claim 10, wherein the set of encoded data slicesincludes at least a write threshold number of encoded data slices. 12.The dispersed storage processing unit of claim 11, wherein the pluralityof primary dispersed storage units is equal to the number of encodeddata slices in the set of encoded data slices.
 13. The dispersed storageprocessing unit of claim 10, wherein the memory further includesinstructions for causing the processor to send a command to one of therespective secondary dispersed storage unit to send one of therespective imposter encoded data slices to one of the respectiveunavailable primary dispersed storage units when the one of therespective unavailable primary dispersed storage units becomesavailable.
 14. The dispersed storage processing unit of claim 13,wherein the memory further includes instructions for causing theprocessor to send a command to the one of the respective secondarydispersed storage units to delete one of the respective imposter encodeddata slices.
 15. The dispersed storage processing unit of claim 13,wherein the memory further includes instructions for causing theprocessor to rename the one of the respective imposter encoded dataslices.
 16. The dispersed storage processing unit of claim 10, whereinthe memory further includes instructions for causing the processor toreceive one of the respective imposter encoded data slices from one ofthe respective secondary dispersed storage units and forward the one ofthe respective imposter encoded data slices to one of the respectiveunavailable primary dispersed storage units when the one of therespective unavailable primary dispersed storage units becomesavailable.
 17. The dispersed storage processing unit of claim 16,wherein the memory further includes instructions for causing theprocessor to send a command to the one of the respective secondarydispersed storage units to delete the one of the respective imposterencoded data slices.
 18. The dispersed storage processing unit of claim16, wherein the memory further includes instructions for causing theprocessor to rename the respective imposter encoded data slice.
 19. Adispersed storage network comprising: a plurality of primary dispersedstorage units; a plurality of secondary dispersed storage units; and adispersed storage processing unit, the dispersed storage processing unitincluding: a communications interface; a memory; and a processor;wherein the memory includes a data segment and wherein the memoryfurther includes instructions for causing the processor to: dispersedstorage error encode a data segment to produce a set of encoded dataslices; for each available primary dispersed storage unit of theplurality of primary dispersed storage units, send a respective writeslice request to a respective available primary dispersed storage unit,the respective write slice request including a respective slice namecorresponding to the respective available primary dispersed storage unitand a respective encoded data slice of the set of encoded data slices,wherein the respective encoded data slice includes a respectiveinformation dispersed algorithm index of the respective availableprimary dispersed storage unit; and for each unavailable primarydispersed storage unit of the plurality of primary dispersed storageunits, send a respective write imposter slice request to a respectivesecondary dispersed storage unit of the plurality of secondary dispersedstorage units, the respective write imposter slice request including arespective imposter slice name corresponding to the respective secondarydispersed storage unit and a respective imposter encoded data slice ofthe set of encoded data slices, wherein the respective imposter encodeddata slice includes a respective information dispersed algorithm indexof the respective unavailable primary dispersed storage unit.
 20. Thedispersed storage network of claim 19, wherein one of the respectivesecondary dispersed storage units periodically attempts to find one ofthe respective unavailable primary dispersed storage units.